<!DOCTYPE html>
<html lang="zh">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
    var i = 20;
    while(i>=1){
        document.write(i-- +"<br>");
    }
    document.write("<hr>");
    var n = 0;
    do{
        document.write(++n+"<br>");
    }while(n<=19);
</script>
</body>
</html>